This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-220990, filed Jul. 21, 2000; No. 2000-222919, filed Jul. 24, 2000; and No. 2001-133464, filed Apr. 27, 2001, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a deflection yoke in a cathode ray tube apparatus such as a color picture tube and a cathode ray tube apparatus provided with the same.
2. Description of the Related Art
A cathode ray tube apparatus, e.g., a color picture tube, comprises a vacuum envelope that includes a glass panel including a substantially rectangular effective portion, a glass funnel connected to the panel, and a cylindrical glass neck connected to the small-diameter portion of the funnel. Formed on the inner surface of the effective portion of the panel is a phosphor screen, which includes a black light-shielding layer and dot- or stripe-shaped three-color phosphor layers that glow blue, green, and red, individually. A shadow mask having a large number of electron beam passage apertures is opposed to the phosphor screen in the vacuum envelope. Further, an electron gun that emits three electron beams is located in the neck, and a deflection yoke is mounted on a yoke mounting portion that is situated ranging from the outer periphery of the neck to the outer peripheral surface of the funnel.
In the color picture tube constructed in this manner, the three electron beams emitted from the electron gun are deflected horizontally and vertically by means of horizontal and vertical deflection magnetic fields that are generated from the deflection yoke, and the phosphor screen is scanned horizontally and vertically through the shadow mask, whereupon a color image is displayed.
A color picture tube of a self-convergence in-line type is widely used as a practical version. According to this color picture tube, an electron gun is constructed as an in-line type that emits three electron beams in a line on one and the same plane. A deflection yoke is designed to generate a horizontal deflection magnetic field of a pincushion type and a vertical deflection magnetic field of a barrel type. The three electron beams emitted in a line from the electron gun can be deflected by means of the horizontal and vertical deflection magnetic fields and concentrated on the whole screen area without requiring any special correcting means.
In the color picture tube constructed in this manner, on the other hand, the deflection yoke is a highly power-consuming element. It is essential, therefore, to reduce the power consumption of the deflection yoke in order to reduce the power consumption of the cathode ray tube. Modern cathode ray tubes are expected to ensure high resolution and improved visibility, and there are many working conditions that require high deflection frequencies. If the deflection yoke is operated with these high deflection frequencies, it releases a plenty of heat. Further, the deflection frequency must be increased in order to cope with application to high-definition monitors of TV sets or personal computers and other OA apparatuses. These situations result in increase in deflecting power and in the heat release of the deflection yoke.
In general, the deflecting power can be lowered by reducing the neck diameter of a cathode ray tube to lessen the outside diameter of a yoke mounting portion on which a deflection yoke is mounted, thereby narrowing the spaces for the action of deflection magnetic fields so that the deflection magnetic fields can efficiently act on electron beams.
In a conventional cathode ray tube apparatus having a yoke mounting portion in the shape of a truncated cone, however, electron beams pass in close vicinity to the inner surface of the yoke mounting portion of a vacuum envelope. Thus, if the neck diameter or the outside diameter of the yoke mounting portion is reduced further, the electron beams run against the inner surface of the yoke mounting portion before they reach a phosphor screen. Inevitably, therefore, the electron beams fail to run against some portions of the phosphor screen that correspond to the maximum deflection angle. If the electron beams continue to run against the inner surface of the yoke mounting portion, moreover, the temperature of the affected portion increases to a level such that glass melts, so that there is a possibility of the vacuum envelope imploding. With use of the conventional cathode ray tube apparatus, therefore, it is hard to lower the deflecting power by further reducing the neck diameter or the outside diameter of the yoke mounting portion.
If a rectangular raster is delineated on the phosphor screen, the region for the passage of the electron beams inside the yoke mounting portion on which a deflection yoke is mounted is substantially rectangular. As means for solving the above-mentioned problems, therefore, there is proposed a yoke mounting portion of a funnel of which the cross section is circular on the neck side and gradually changes into a substantially rectangular shape as the panel is approached.
If the yoke mounting portion of the funnel is thus formed substantially in the shape of a truncated pyramid, the diameters of the yoke mounting portion in the respective directions of its major (horizontal) and minor (vertical) axes can be shortened without changing the diagonal diameter corresponding to the widest deflection angle. Thus, the horizontal and vertical deflection coils of the deflection yoke can be brought close to the electron beams, so that the electron beams can be deflected efficiently, and the deflecting power can be lowered.
On the other hand, there are various types of deflection yokes, including a saddle-saddle type such that both horizontal and vertical deflection coils are of a saddle type, a semi-toroidal type such that horizontal and vertical deflection coils are of saddle and toroidal types, respectively, etc. A saddle-saddle deflection yoke described in Jpn. Pat. Appln. KOKAI Publication No. 11-265666, for example, comprises a pair of saddle-type horizontal deflection coils in the shape of a truncated pyramid located inside a separator formed of an insulator, a pair of saddle-type vertical deflection coils located outside the separator, and a magnetic core in the form of a truncated pyramid located externally covering the vertical deflection coils.
In the saddle-saddle deflection yoke having the basic construction described above, the deflecting power can be made lower than in a semi-toroidal deflection yoke. It is difficult, however, to form the magnetic core in the shape of a truncated pyramid, and the vertical deflection coils cannot be toroidally wound on the core of this shape with ease. Thus, the deflection yoke entails high manufacturing cost and lacks in general-purpose properties.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a deflection yoke capable of reduction in deflecting power and manufacturing cost and a cathode ray tube apparatus provided with the same.
In order to achieve the above object, a deflection yoke according to an aspect of the present invention comprises: a pair of saddle-type horizontal deflection coils located symmetrically with respect to a central axis on the opposite sides of a horizontal axis perpendicular to the central axis, individually, and substantially in the shape of a truncated pyramid as a whole; a magnetic core substantially in the shape of a truncated cone located coaxially with the central axis and surrounding the horizontal deflection coils; and a pair of vertical deflection coils wound on the magnetic core, the horizontal deflection coils and the magnetic core being arranged so that a relation between a space vf between the large-diameter end portion of the magnetic core and each of the horizontal deflection coils and a space vr between the small-diameter end portion of the magnetic core and each of the horizontal deflection coils, with respect to the direction of a vertical axis perpendicular to the central axis and the horizontal axis as viewed in the direction of the horizontal axis, is given by vfxe2x89xa7vr.
Further, a deflection yoke according to another aspect of the invention comprises a pair of saddle-type horizontal deflection coils located symmetrically with respect to a central axis and substantially in the shape of a truncated pyramid, a magnetic core substantially in the shape of a truncated cone located coaxially with the central axis and surrounding the horizontal deflection coils, and a pair of vertical deflection coils wound on the magnetic core, the horizontal deflection coils and the magnetic core being arranged so that a minimum space portion in which the space between the magnetic core and each of the horizontal deflection coils in the direction of a horizontal axis perpendicular to the central axis of each horizontal deflection coil has a minimum is provided near the small-diameter end portion of the core and that the space between the core and each horizontal deflection coil enlarges continuously from the minimum space portion to the large-diameter end of the core.
Furthermore, a deflection yoke according to another aspect of the invention comprises a pair of saddle-type horizontal deflection coils located symmetrically with respect to a central axis and substantially in the shape of a truncated pyramid, a separator located outside the horizontal deflection coils and substantially similar to the horizontal deflection coils in shape, a magnetic core substantially in the shape of a truncated cone located coaxially with the central axis and surrounding the separator, and a pair of vertical deflection coils wound on the magnetic core, the horizontal deflection coils and the magnetic core being arranged so that a minimum space portion in which the space between the magnetic core and the separator in the direction of a horizontal axis perpendicular to the central axis of each horizontal deflection coil has a minimum is provided near the small-diameter end portion of the core and that the space between the core and the separator enlarges continuously from the minimum space portion to the large-diameter end of the core.
A cathode ray tube apparatus according to an aspect of the present invention comprises: a vacuum envelope including a panel with a phosphor screen formed on the inner surface thereof, a funnel connected to the panel, and a cylindrical neck connected to the small-diameter end of the funnel, and formed having a yoke mounting portion in the shape of a truncated pyramid covering the outer periphery from the neck to the funnel; an electron gun located in the neck of the vacuum envelope and configured to emit electron beams toward the phosphor screen; and a deflection yoke mounted on the outside of the yoke mounting portion and configured to deflect the electron beams.
According to the deflection yoke and the cathode ray tube apparatus described above, the horizontal deflection coils are arranged substantially in the shape of a truncated pyramid. Therefore, electron beams can be deflected efficiently, so that the deflecting power can be lowered. With use of the magnetic core substantially in the shape of a truncated cone, moreover, the deflection yoke can be manufactured easily. Further, the heat dissipation property can be improved, so that heat release of the deflection yoke can be restrained.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.